[web] introduce user-profile as a menu variant

Summary:
The first step to introducing the user profile menu is that we need to create a user-profile className variant in Menu. This className handles things like the menu background color, the placement, and the color of the content

Screenshot of designs:

Part of https://linear.app/comm/issue/ENG-5225/introduce-userprofilemenu

Depends on D9455

Test Plan:
Please see the screenshot below to see what the container of the menu looks like

Reviewers: atul, inka

Reviewed By: atul

Subscribers: ted, ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9456